Because electrostatic forces are crucial in biological systems, molecular dynamics simulations of biological systems require a method of computing electrostatic forces that is accurate and rapid. We propose a surface charge method, apply it to a system of arbitrary number of charged dielectric spheres, and obtain an exact solution for an arbitrary configuration of the spheres. The precision depends only on the number of terms kept in a series expansion and can therefore be controlled at will. It appears that the first few terms are usually adequate. The exact result exhibits a phenomenon that we call asymmetric screening. Namely, the magnitude of attractive interactions is decreased (relative to point charges in an infinite solvent) while the magnitude of repulsive interactions is increased (again, relative to point charges in an infinite solvent). This effect might aid in the adoption of correct conformations and in intermolecular recognition. Evaluation of the energy involves only matrix inversion. The surface charge method can be transformed easily to a numerical method for use with arbitrary surfaces. With modest additions, the model also describes an electrorheological fluid. Such a system provides the cleanest opportunity to apply the model.